DESCRIPTION RNA is involved in catalysis of the essential processes of translation and mRNA splicing. The complexes that catalyze these processes (the ribosome and spliceosome) also contain protein, which is proposed to function largely or entirely by stabilizing the active structures and facilitating conformational changes of the RNA components. To understand the means by which RNA can accelerate multi-step reactions and protein might facilitate catalysis by RNA, it is important to understand the intrinsic capabilities and limitations of RNA at performing conformational rearrangements. RNA alone accelerates the two-step splicing reaction of a group I performing conformation rearrangements. RNA alone accelerates the two-step splicing of a group I performing conformation rearrangements. RNA alone accelerates the two-step splicing reaction of a group I intron from Tetrahymena thermophila, rendering this an ideal model system for detailed study. A conformational change occurs between the two chemical steps that positions the 3'-splice site for cleavage. Interactions that are broken and formed during the course of this rearrangement will be identified using kinetic approaches and chemical probing, and the kinetics of individual base- pairing changes that occur as the 3-splice site enters the active site will be determined using a fluorescence approach. It is hoped that a detailed understanding of a single conformation change in RNA will advance our understanding of RNA dynamics more generally.